Remarkable catalytic activity of calcined pitch based activated carbon fiber for oxidative removal of SO₂ as aqueous H₂SO₄

Catalytic activity of a series of pitch-based activated carbon fibers (ACFs) was examined at room temperature for the oxidative removal of SO₂ as aqueous H₂SO₄ which was continuously recovered at steady state. Calcination up to 900 °C in an inert atmosphere increased the activity very markedly regardless of the ACF; however, higher temperatures up to 1200 °C increased the activity of ACFs with larger surface area (1000 m²/g) while the ACFs with smaller surface area lost activity very sharply. ACF with the largest surface area and calcined at 1100 °C resulted in the complete capture of 1000 ppm SO₂ by ACF weigh/flow rate (W/F) 1 × 10^-3 g·min/mL under 10% H₂O. Lower humidity reduced the activity, although larger W/F allowed complete removal of SO₂. TPDE measurements revealed CO evolution from the ACF in the range of 400-1100 °C, the amount and the range depending on the ACF. ACF with the highest activity appeared to be obtained when the major CO-evolving groups were removed before marked reduction of the surface area took place. ACF that evolved CO more exhibited higher activity. The active site produced by CO evolution is discussed briefly.